1. Field of the Invention
The present invention relates to a tilt steering apparatus for vehicle, mounted with a tilt lock mechanism capable of adjusting the height of the steering wheel of the vehicle according to the physical figure (physique) or driving posture of a driver.
2. Description of the Related Art
A tilt steering apparatus mounted with a tilt lock mechanism is disclosed in a number of publications, for example, U.S. Pat. Nos. 6,481,310, 6,282,977, 5,452,624, 5,143,402, 5,078,022, 4,903,540, and 4,892,330; Japanese Patent Publications Nos. 2000-272524, 1999-268654, 1999-208483, 1999-198819, 1999-129914, 1998-138934, 1996-230687; and Japanese Utility Model Publications Nos. 1994-1110, 1991-112468,1989-51567, 1988-52666, 1988-012470, 1985-144569, and 1982-142677.
The tilt lock mechanism introduced in the above publications is composed of a fixed gear, a movable gear, a wedge member (or lock slider) and a reaction member, which are sequentially disposed perpendicular to an operating plane of the movable gear. In particular, the tilt lock mechanism mounted on the steering apparatus discussed in U.S. Pat. No. 628,977, as shown in FIGS. 1 and 2, is composed of a fixed gear 31, a movable gear 32 upon the fixed gear 31, a wedge member 33 disposed at the lower portion of the movable gear 32 in such a manner to be able to slide, and a reaction member 35 for supporting a bottom surface of the wedge member 33.
With the help of such tilt lock mechanism, the movable gear 32 is locked or released as follows. Referring to FIG. 1 first, if a tilt lever 34b is rotated clockwise, a protruded portion 32b of the wedge member 33 correspondingly slides to the right side, and the movable gear 32 is released from the tooth coupling to the fixed gear 31. When the lock is released, an upper column member 15 is tilted with respect to a lower column member 15 so as to set the steering wheel at an appropriate height. On the other hand, if the tilt lever 34b is freed, the tilt lever 34b is rotated counter-clockwise by a spring 30, and the wedge member 33 slides to the left side, sliding in-between the movable gear 32 and the reaction member 35, and pushes the movable gear 32 up to be toothed on the fixed gear 31. In this way, the height of the steering wheel can be adjusted as desired.
However, the tilt lock mechanism discussed above has the following defects.
First of all, the manufacturability of the tilt lock mechanism is low, in other words, the work of manufacturing has a low efficiency, because the reaction member with a complicated shape needs to be interruptedly formed to the upper column member 15.
Secondly, since a protrusion 32c is disposed at the top end side of the movable gear 32, when the gear is unlocked, the protrusion 32c is usually exposed from the upper column member 14 to be pivoted. This often hurts the driver's knee(s). Although a manufacturer might try to set the upper column member 14 near to the driver's seat in order to prevent the protrusion 32c from being exposed from the upper column member 14, this only makes the space around the driver's knees smaller, interfering the driving.
Thirdly, although the tilt lever 34b is in a position for locking the movable gear 32, if the tilt lever 34b rotates more or less than it is supposed to in the locking position because of a minor error in the manufacture of components, or if the tilt lever 34b rotates, the wedge member 33 coupled to the tilt lever 34b as one body rotates in a horizontal direction and at the same time, does the vertical rectilinear motion. As a result, the protruded rear surface 32b of the movable gear 32 and the wedge member 33 inevitably make a point contact, not a line contact, and thus the supporting rigidity and abrasion resistance of both components is deteriorated.
Fourthly, because the protruded portion on the lower end of the wedge member 33 is too little, a heavy load is often placed on the wedge member 33 for breaking or disengaging the pivotable from the fixed gear. This is actually the major cause of changes in operational load or overload on the tilt lever for lock release, i.e. disengaging the gears from each other. As a result, the operability of the tilt lever is substantially lowered.
As an attempt to resolve the above problems, U.S. Pat. No. 5,143,402 disclosed a modified tilt lock mechanism as illustrated in FIGS. 3 and 4. The tilt steering apparatus in this invention is comprised of a fixed gear 9′, a movable gear 12′, plates 28′ with a circular arc-shaped slot 31′, disposed at the both sides of the movable gear 12′ and the fixed gear 9′, a shaft 30′ to be inserted into the slot 31′, and a tilt lever 27′ for driving the shaft 30′.
This tilt lock mechanism 30′, by the operation of the tilt lever 27′, translates vertically while rotating in the horizontal direction at the same time. As such, the rear surface of the movable gear 12′ and the shaft 30′ make the point contact, not the line contact, and this consequently deteriorates supporting rigidity and abrasion resistance.
Also, the slot 31′ in a circular-arc shape makes the work of manufacturing more difficult.